1. Field of the Invention
The present invention relates to the design of a dual source solar and thermal power generation plant that provides practical yet reliable power generation at low cost. In particular, the present invention relates to the design of a power plant with solar collectors and associated thermal power generating equipment, utilizing the proposed particular solar energy collectors, pressurizers, heat exchanger, auxiliary boiler/steam superheater, turbine-generator, generator frequency synchronizer, step-up transformer, switchyard and all thermal power generation supporting equipment. The scope of the invention includes the combination of the solar energy collector, main power plant equipment, and the power output facility to the outside power grid, to provide a complete power generation facility.
In the field of solar thermal power plants there are currently some other designs that make use of components such as parabolic solar collector, or reflecting mirror type. However, these other designs may have high cost or low efficiency concerns. The inventor's proposed design is intended to overcome these concerns.
2. Discussion of Related Art
The amount of solar energy that falls on the surface of earth per minute is equivalent to burning 100,000,000 tons of coal per minute. The average solar energy per square centimeter (cm) on the earth's surface per minute is about 2 calories. This is equivalent to 4,423 BTU per square foot per day. The solar energy received on each individual area will be different depending on the clouds, moisture in atmosphere, dust in the air, location and season. In the southwestern United States from Las Vegas to the Mexican border along the Colorado River, the solar energy per square foot is between 1880 to 2000 BTU per square foot per day. This is the highest BTU number among all areas in the United States. This is because the region is a desert area, and the air is extremely dry. This area has an average of over 300 sunny days per year. The area starting from Las Vegas along the Colorado River to the Mexico border and extended 150 miles each to the west and to the east from the river encompasses approximately 60,000 square miles. Of that area, by estimation, approximately 20%, or about 12,000 square miles (about 7,680,000 acres), is useful for solar collection. The potential in this desert area could accommodate 200 or more of 300 mega Volt-Ampere (MVA) size solar power plants. The total amount of power generated is sufficient to supply the power demands of the west coast and southwestern United States. With this kind of power potential, the construction of solar power plants in this area should be actively pursued. Building new power transmission lines to handle the generated power should also be considered.
With an estimation that only 60 more years of world oil supply, 80 more years of available nuclear fuel, 80 years of natural gas reserves and 300 more years of coal supply are left, the potential of solar energy in this area should be actively developed. If this were to be done, there would be no need for building additional coal or nuclear power plants.
Solar power could save the United States from the difficult problems of mining and refining the uranium for nuclear power fuel, treating and handling of unwanted spent nuclear fuel, greatly reducing the nuclear radiation harm to humans and the environment. It could also reduce the emission of additional CO2 which is generated by burning coal in coal power plants, reducing pollutants and mitigating the life and environment-threatening problem of global warming.
The development of large scale solar power technology is a relatively new trend in the industry. Many solar power projects have been planned and/or initiated with a large amount of investment. However, the results have not met expectations. The progress of solar power generation technology has been less than expected. The returns on invested capital are mostly lower than the original investment. At present, the price of power generation by fossil fuel is still lower than by solar power. This is true especially for the photovoltaic type power plant. Many photovoltaic solar power plants have been abandoned during construction, or after short-term operation. Generally, bankers are hesitant to commit capital to solar power plant projects because the capital returns are less than anticipated. This is a disadvantage for harnessing solar power. The vast amount of solar energy that could be realized in this area has not been developed. A huge amount of potential solar energy is being wasted every day. This invention is designed to overcome these hardships and gives a way to increase the use of solar energy, harnessing solar energy more effectively and practically, until the technology progresses to a point where new ways of more efficient and practical use of solar power are discovered.
The photovoltaic solar power technology has gained considerable progress. It is now able to utilize 12 to 15 percent of incoming solar energy. Yet this is far below the 35% efficiency of a nuclear power plant, or 38% for a fossil power plant. The majority of the solar energy is not effectively used by photovoltaic technology, as there are several disadvantages in the present photovoltaic technology. First, the silicon film of its main component is delicate and expensive to manufacture. At least seven different films are needed to make a final product of silicon plate. The silicon film is only a semi-conductor. It cannot pass a large amount of electric current. A copper or aluminum conductor mesh or net is required for taking the electrical current out. The electrical current produced is of low voltage and (low) milli-ampere current. Therefore a high number of silicon plates must be needed to make the current large enough to be meaningful. On top of this, only a narrow band of photo wavelength of sunlight can excite the electrons in the film to produce current. Overall, the produced current is of low voltage and low current. In addition, the produced current is a direct current (DC). The DC power generated in this system is not suitable for long-distance transmission to electrical power users because the DC current is not suitable for long distance transmission. So the DC current has to be converted to AC (alternate current), in order to be transmitted to the far-end power users. Each step of conversion increases power loss and adds to the overall cost. The total equipment cost of a photovoltaic solar power system would be too high for a large power output, for example, from one to 300 mega-watts (MW) class power plant. The plant would be economically prohibitive and the rate of solar energy utilization would be low. The efficiency is also low. Worse, under strong bombardment of ultra-violet (UV) radiation from the sun, the high cost silicon solar panels deteriorate rapidly. The deteriorated silicon plates would need to be replaced regularly. This would happen before the investment capital could be recovered. Therefore, a large output photovoltaic power plant is not commercially practical today. Many plants have previously been planned, built, and then abandoned. Those are examples of failed economical activities. A solar power plant output of more than 300 MW is considered impractical considering that a large area of land is required and the cost is high.
The next choice is the solar thermal power plant. As mentioned in paragraph [0002], the mirror reflection type and the parabola solar receiver type have been designed and some are in operation. The results are not encouraging. Some have been abandoned and some are operating with high cost and low efficiency. For two examples, a parabola solar receiver type power plant with 150 MW in the Mojave Desert, Calif. had been abandoned; and the Ivanpar mirror reflection type solar thermal power plant costs $2.2 billion for an output of 395 MW, the cost is too high as prohibiting. In this specification a particular design is proposed for a new type of dual energy solar thermal power plant. It is a steam turbine-generator power plant using a combination of solar energy collectors and a small auxiliary boiler/steam superheater. The objectives for the invention of this plant are to be efficient, cost effective, practical and reliable.
For a low temperature turbine set as proposed to be used in this design, a minimum steam temperature of 680° F. (360° C.) is required to drive the turbine. This is difficult to achieve by the proposed solar collector alone because the received solar rays alone cannot deliver quickly and consistently the large amounts of energy required to drive a turbine continuously. The quantity of incoming solar energy is not as large as the thermal energy coming from a nuclear reactor or a coal fired boiler as used in a coal fired power plant. To compensate for the insufficient thermal energy provided by solar rays alone for driving the turbine, an auxiliary boiler/steam superheater is needed to supply additional heat in addition to the collected solar heat. This would guarantee stable long-term turbine operation. See FIG. 8. The facility built based on this design could also be used for power generation during cloudy or raining days.
A frequently asked question is, where would the power come from at night if solar power becomes the main power source? The answer to this question would be the combination of hydropower, enlarged battery facility, and stored thermal energy in a liquid salt container facility, plus the fact that the night power demand is low after 10 PM. The auxiliary boiler as proposed in this specification can also be used to generate small amounts of power for short periods.
The design proposed in this specification offers advantages of: (1) lower cost because the design is simple, and the equipment used are mostly common in the market with reasonable costs; (2) high efficiency because the proposed solar collector will take in all solar heat available; (3) reliable because all equipment is commonly available with proven good operational records; and (4) practical because there is no unreasonable design, uncommon equipment, or unreasonable operation procedures. These are the advantages offered by this system design over other types of solar thermal power plants such as the parabola solar collector type, or the mirror reflection solar collector type.
The auxiliary boiler/steam superheater will require burning low amounts of natural gas to supply about 20% or the balance of the required heat. But the advantage is that this heat is being used to harness large amounts of unrealized no-cost solar power continuously when it is integrated with the solar energy collector. If the auxiliary boiler is not added, 0% of solar power can be used in this facility. The choice is obvious.
Newly developed technology of “fracking” for mining natural gas has increased production of natural gas. It has been said that the gas can last for the next 100 years. If carefully planned and combined with the solar energy collecting system proposed in this specification, the gas availability could be extended to 500 years. By that time, additional new technologies may be discovered for obtaining needed energy.
In the rate of conversion of solar energy to electricity, it is estimated that an area of about 600 acres is required for a 300 MVA solar thermal power plant. Two hundred such plants would supply an output of 60,000 MVA, enough to supply the total new power demands of the entire west coast of the United States while retiring all nuclear power plants and the coal fire power plants.
When this energy corridor is developed in the southwest United States using the proposed power generation design, the electricity will become abundant and it will support the automobile electrification, further mitigating the air pollution for the country.
The three most important engineering considerations for a solar thermal power generation plant are: (1) harvesting the solar energy, (2) preserving the harvested solar energy, and (3) utilizing the solar energy.
First, the necessary technical aspect is how to collect and absorb the solar energy efficiently; and the next is how to preserve the collected energy without losing it.
Finally the collected and preserved solar energy should be able to be utilized to generate electrical power. In this invention, it is proposed to use the collected solar heat to heat water or another heating medium to the required temperature such that the final product, the heated steam, has sufficient pressure to drive the turbine-generator set within a solar thermal power plant. The sufficient steam temperature to drive the turbine is estimated at about 680° F. (360° C.).
As mentioned above, low cost, efficiency, reliability and practicality are the main objectives of this invention. It is necessary that the plant cost be reasonable and the plant is robust for long-term operation. Otherwise, it would not be practical for the capital investment. It would not be feasible to build a solar thermal power plant if the equipment, labor and fuel costs are too high. There have been too many high capital solar power plants abandoned because of high cost, low efficiency, or short duration of effective operation time. The economics of the plant and long-term effective operation are crucial to make the plant practical.